CN108009383B - Method and system for determining appearance of natural laminar flow nacelle - Google Patents

Method and system for determining appearance of natural laminar flow nacelle Download PDF

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CN108009383B
CN108009383B CN201711431004.5A CN201711431004A CN108009383B CN 108009383 B CN108009383 B CN 108009383B CN 201711431004 A CN201711431004 A CN 201711431004A CN 108009383 B CN108009383 B CN 108009383B
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nacelle
variable group
engine
obtaining
variable
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CN108009383A (en
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陶洋
熊能
林俊
刘志勇
张兆
范长海
刘光远
张诣
郭秋亭
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Ultra High Speed Aerodynamics Institute China Aerodynamics Research and Development Center
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Abstract

The invention discloses a method and a system for determining the appearance of a natural laminar flow nacelle. The method comprises the following steps: parameterizing the section of the nacelle to be improved by adopting a CST method through gamma-ReθThe transition model acquires the transition position of the natural laminar flow nacelle; acquiring boundary conditions of an inlet of an air inlet channel and an outlet of an engine; obtaining a variable group by adopting a Latin square design method; acquiring corresponding nacelle resistance according to the variable group; establishing a first Kriging response surface model; acquiring the variance of the nacelle resistance corresponding to the variable group; establishing a second Kriging response surface model; determining an objective function, and predicting the mean value and the variance of the nacelle resistance by using a first Kriging response surface model and a second Kriging response surface model; obtaining a variable group when the function value of the objective function is minimum, and obtaining an optimal variable group; and determining the shape of the natural laminar flow nacelle according to the parameters in the optimal variable group. The method and the system can effectively improve the appearance performance of the laminar flow nacelle, reduce the surface friction resistance of the airplane and improve the economy of the airplane.

Description

Method and system for determining appearance of natural laminar flow nacelle
Technical Field
The invention relates to the field of airplane nacelle design, in particular to a method and a system for determining the appearance of a natural laminar flow nacelle.
Background
The development of large-scale transport aircraft is the most competitive field of the international aviation industry, and the challenge is how to meet the increasingly strict requirements in the aspects of economy, safety, comfort, environmental protection and the like. For example, the oil consumption of the civil transport plane of the third generation in the future of NASA project in the united states is reduced by 33%, 40% and 70% respectively compared with the current B737, and it is necessary to develop design studies for improving the aerodynamic efficiency of the plane in response to these severe requirements.
Reducing aerodynamic drag has been one of the most active research hotspots in the aerodynamic community, and the results of the a340 study show that a drag reduction of 0.3% corresponds to a saving of 300 kg of fuel or an increase of 3 passengers. Because the friction resistance of the large subsonic transport plane of the wing body assembly accounts for about 50% of the whole plane resistance, the reduction of the plane resistance by adopting the laminar flow technology is a very important subject in layout optimization. Studies by NASA Obara et al have shown that by expanding laminar flow at the surface of a typical commercial airliner, it is possible to reduce the total aircraft drag by (12-14)%. Resistance was reduced by 4.7% in the a380 design by introducing advanced laminar flow techniques.
With the rapid development of the technology of the turbofan engine with the large bypass ratio, the increase of the geometric dimension of the turbofan engine leads to the rapid increase of the proportion of the resistance of the engine nacelle in the full engine resistance, and the surface friction resistance of the nacelle is one of the main resistance sources of the nacelle. Studies by NASA Obara et al indicate. Under the cruising condition of a large airplane, the surface friction resistance of the engine nacelle contributes about 80 percent of the nacelle resistance and accounts for about 3 percent of the full-airplane resistance. Therefore, laminar flow with a certain length is realized on the outer surface of the nacelle, which is beneficial to reducing the surface friction resistance of the airplane and improving the economy of the airplane.
Disclosure of Invention
The invention aims to provide a method and a system for determining the shape of a natural laminar flow nacelle so as to determine the shape of the natural laminar flow nacelle, thereby reducing the surface friction resistance of an airplane and improving the performance of the airplane.
In order to achieve the purpose, the invention provides the following scheme:
a method of determining a natural laminar flow nacelle contour, the method comprising:
parameterizing the section of the nacelle to be improved by adopting a CST method to obtain a plurality of parameter sets; each parameter group comprises different values of a plurality of parameters; the nacelle to be improved is a non-layer fluidization nacelle;
by gamma-ReθThe transition model acquires the transition position of the natural laminar flow nacelle;
acquiring boundary conditions of an inlet of an air inlet channel and an outlet of an engine;
updating the parameter groups by adopting a Latin square design method to obtain a plurality of variable groups; each parameter group correspondingly obtains a variable group;
obtaining the nacelle resistance corresponding to each variable group according to the variable groups;
establishing a first Kriging response surface model according to the variable groups and the corresponding nacelle resistance;
obtaining the variance of the nacelle resistance corresponding to each variable group according to the first Kriging response surface model;
establishing a second Kriging response surface model according to the variable groups and the corresponding variances;
determining an objective function
Figure BDA0001524888630000021
Wherein
Figure BDA0001524888630000026
Represents the mean value of the nacelle resistance corresponding to the ith variable group,
Figure BDA0001524888630000022
representing the variance of the nacelle resistance corresponding to the ith variable group;
predicting the mean value and the variance of the nacelle resistance by using the first Kriging response surface model and the second Kriging response surface model;
obtaining a variable group when the function value of the objective function is minimum, and obtaining an optimal variable group;
and determining the shape of the natural laminar flow nacelle according to the parameters in the optimal variable group.
Optionally, obtaining boundary conditions of the inlet of the intake duct and the outlet of the engine specifically includes:
according to
Figure BDA0001524888630000023
Obtaining boundary conditions of inlet of air inlet passage
Figure BDA0001524888630000024
Wherein
Figure BDA0001524888630000025
A unit normal vector pointing to the outside of the flow field at the inlet of the engine; mfMach number at the inlet of the engine; p is a radical offIs the pressure value at the inlet of the engine, pfIs the fluid density at the engine inlet; gamma is gamma-ReθIntermittent factors in transition models;
according to
Figure BDA0001524888630000031
Obtaining boundary conditions of an engine outlet
Figure BDA0001524888630000032
Wherein
Figure BDA0001524888630000033
A unit normal vector pointing to the interior of a flow field at an outlet of the engine; p is a radical ofexIs the pressure value, p, of the engine outletexIs the fluid density at the engine outlet; t is0,exIs the total temperature of the engine exhaust gases.
Optionally, the obtaining of the nacelle resistance corresponding to each variable group according to the plurality of variable groups specifically includes:
and acquiring the nacelle resistance corresponding to each variable group by adopting a structured grid and a three-dimensional NS equation.
Optionally, the structured grid specifically includes:
setting a plurality of grid boundary conditions based on a wake vortex transmission method, and taking a wake vortex field obtained by calculation under the free boundary condition as the boundary condition of a rear calculation grid;
dividing the simulation object into a plurality of subproblems, and setting up calculation grids and turbulence models with different densities for different objects.
Optionally, after obtaining the variable group that minimizes the function value of the objective function and obtaining the optimal variable group, the method further includes:
at the optimal variable group, detecting the mean value of the nacelle resistance predicted by the first Kriging response surface model and the variance of the nacelle resistance predicted by the second Kriging response surface model according to an NS equation, and judging whether the convergence standard is met or not to obtain a first judgment result;
when the first judgment result shows that the convergence criterion is met, taking the optimal variable group as a final optimal variable group;
and when the first judgment result shows that the convergence standard is not met, increasing the parameters in the parameter group, and returning to the step of acquiring the nacelle resistance corresponding to each variable group according to the plurality of variable groups.
Optionally, the obtaining a variable group that minimizes the function value of the objective function to obtain an optimal variable group specifically includes:
and performing optimization solution by adopting an EGO (global optimization algorithm) to obtain a variable group when the function value of the objective function is minimum.
A system for determining the profile of a nacelle using natural laminar flow, said system being adapted for use in the method described above, said system comprising:
the parameterization module is used for parameterizing the section of the nacelle to be improved by adopting a CST method to obtain a plurality of parameter sets; each parameter group comprises different values of a plurality of parameters; the nacelle to be improved is a non-layer fluidization nacelle;
a transition occurrence position acquisition module for passing gamma-ReθThe transition model acquires the transition position of the natural laminar flow nacelle;
the boundary condition acquisition module is used for acquiring boundary conditions of an inlet of an air inlet channel and an outlet of an engine;
a variable group obtaining module, configured to update the parameter groups by using a latin square design method to obtain a plurality of variable groups; each parameter group correspondingly obtains a variable group;
the nacelle resistance acquiring module is used for acquiring nacelle resistance corresponding to each variable group according to the variable groups;
the first Kriging response surface model building module is used for building a first Kriging response surface model according to the multiple variable groups and the corresponding nacelle resistance;
the variance obtaining module is used for obtaining the variance of the nacelle resistance corresponding to each variable group according to the first Kriging response surface model;
the second Kriging response surface model building module is used for building a second Kriging response surface model according to the multiple variable groups and the corresponding variances;
an objective function determination module for determining an objective function
Figure BDA0001524888630000041
Wherein
Figure BDA0001524888630000043
Represents the mean value of the nacelle resistance corresponding to the ith variable group,
Figure BDA0001524888630000042
representing the variance of the nacelle resistance corresponding to the ith variable group;
the prediction module is used for predicting the mean value and the variance of the nacelle resistance by utilizing the first Kriging response surface model and the second Kriging response surface model;
an optimal variable group obtaining module, configured to obtain a variable group when a function value of the objective function is minimized, and obtain an optimal variable group;
and the natural laminar flow nacelle shape determining module is used for determining the shape of the natural laminar flow nacelle according to the parameters in the optimal variable group.
Optionally, the boundary condition obtaining module specifically includes:
an inlet boundary condition acquisition unit for acquiring inlet boundary condition of air inlet channel based on
Figure BDA0001524888630000051
Obtaining boundary conditions of inlet of air inlet passage
Figure BDA0001524888630000052
Wherein
Figure BDA0001524888630000053
A unit normal vector pointing to the outside of the flow field at the inlet of the engine; mfMach number at the inlet of the engine; p is a radical offIs the pressure value at the inlet of the engine, pfIs the fluid density at the engine inlet; gamma is gamma-ReθIntermittent factors in transition models;
an engine outlet boundary condition acquisition unit for obtaining a boundary condition based on
Figure BDA0001524888630000054
Obtaining boundary conditions of an engine outlet
Figure BDA0001524888630000055
Wherein
Figure BDA0001524888630000056
A unit normal vector pointing to the interior of a flow field at an outlet of the engine; p is a radical ofexIs the pressure value, p, of the engine outletexIs the fluid density at the engine outlet; t is0,exIs the total temperature of the engine exhaust gases.
Optionally, the nacelle resistance obtaining module obtains nacelle resistance corresponding to each variable group by using a structured grid and a three-dimensional NS equation.
Optionally, the system further includes:
the judging module is used for obtaining a variable group when the function value of the objective function is minimum, detecting the mean value of the nacelle resistance predicted by the first Kriging response surface model and the variance of the nacelle resistance predicted by the second Kriging response surface model at the optimal variable group according to an NS equation, judging whether the convergence standard is met or not, and obtaining a first judging result;
a final optimal variable group determination module, configured to, when the first determination result indicates that a convergence criterion is satisfied, take the optimal variable group as a final optimal variable group;
and the parameter updating module is used for increasing parameters in the parameter group when the first judgment result shows that the convergence standard is not met, and returning to the step of acquiring the nacelle resistance corresponding to each variable group according to the plurality of variable groups.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the natural laminar flow nacelle appearance determining process relates to the simulation of a great deal of complicated processes, for example transition, roughness simulation etc. natural laminar flow mainly obtains favorable pressure gradient through the profile determination of aircraft appearance, inhibits flow direction TS ripples to increase to postpone transition, this kind of transition is very easily restricted by the flight condition, can influence the performance of aircraft at non-design operating mode.
The laminar flow nacelle has the trouble of uncertainty factors such as surface roughness in actual use, firstly, the roughness caused by processing errors and a link structure is difficult to avoid, secondly, impact and erosion of wind, frost, rain, sand, mosquitoes and the like exist in the using process, and the surface roughness is obviously influenced by long-term accumulation and long-term accumulation, so that the sensitivity and influence of the laminar flow nacelle are considered in the shape determining process, the performance of the shape of the laminar flow nacelle is effectively improved, the surface friction resistance of an airplane is reduced, and the economy of the airplane is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic flow chart of a method for determining the shape of a nacelle according to the invention;
FIG. 2 is a schematic structural diagram of a system for determining the profile of a nacelle according to the invention;
FIG. 3 is a schematic view of the natural laminar flow nacelle according to the present invention;
FIG. 4 is a comparison of the upper section generatrices of the nacelle to be modified of the present invention with the modified natural laminar flow nacelle;
FIG. 5 is a comparison of the lower section generatrix of the nacelle to be modified of the present invention with the modified natural laminar flow nacelle;
FIG. 6 is a graph showing a comparison of the distribution of the coefficients of frictional resistance of the upper, lower and side surfaces of the nacelle to be modified and the modified natural laminar flow nacelle according to the present invention;
FIG. 7 is a cloud chart of the coefficient of friction drag of the nacelle surface to be improved according to the invention;
FIG. 8 is a cloud chart of the coefficient of friction resistance of the surface of the nacelle with natural laminar flow after the improvement of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a schematic flow chart of a method for determining the shape of a natural laminar flow nacelle according to the present invention. As shown in fig. 1, the method includes:
101, the step of: the profile (cross section) of the nacelle to be improved is parameterized by the CST method. This step obtains a plurality of parameter sets; each parameter group comprises different values of a plurality of parameters; the nacelle to be improved is a non-laminar fluidized nacelle. The three typical profiles of the upper part, the lower part and the side lower part of the improved nacelle are parameterized by adopting a CST (class function/shape function transformation) method, the outline of the nacelle is described by using a limited parameter set (for example, one parameter set comprises 21 parameters, and the value range of each parameter is from 0 to 1), and one group of determined parameter sets corresponds to one determined new outline, so that a plurality of parameter sets correspond to the outlines of a plurality of nacelles, the modified outline of the nacelle is obtained by incremental difference, and the accurate description of the outline characteristics of the nacelle by using fewer parameters can be realized.
Step 102: by gamma-ReθThe transition model acquires the position of transition of the natural laminar flow nacelle. The transition calculation adopts the gamma-Re developed by Menter et alθThe transition model does not pursue a specific complex physical process for simulating transition, and controls the generation of an intermittent factor in the boundary layer through an empirical correlation function and a transition momentum Reynolds number so as to determine the position of transition occurrence.
Step 103: boundary conditions of an inlet of the air inlet channel and an outlet of the engine are obtained. Boundary conditions of the inlet of the air inlet and the outlet of the engine are established according to adiabatic isentropic conditions and flow uniformity assumptions. The specific process is as follows:
far-field incoming flow and wall boundary conditions:
giving corresponding far-field boundary conditions by giving the velocity, pressure and density of the incoming flow; for the wall, a wall boundary condition without slip is adopted.
Inlet boundary conditions of the inlet:
for a port inlet, the boundary conditions are given by the engine state, the mass flow that would normally enter the engine operating state
Figure BDA0001524888630000081
As the given parameter. For the calculation of the outflow, the mass flow is that of the flow fieldOutlet conditions. The specific method is that the far field coming to the inlet of the engine meets the adiabatic isentropic condition and the flow is uniform, and the mass flow rate is as follows:
Figure BDA0001524888630000082
in the formula, the subscript "f" represents the engine inlet parameter, the subscript "0" represents the stagnation parameter in the far field, and the subscript "∞" represents the parameter of the incoming flow in the far field. In the above formula, the unknown number is only the Mach number M of the inlet of the enginefBy iteration, M can be calculatedfFurther, the corresponding flow parameters can be derived:
Figure BDA0001524888630000083
Figure BDA0001524888630000084
then use
Figure BDA0001524888630000085
Obtaining boundary conditions of inlet of air inlet
Figure BDA0001524888630000091
Wherein
Figure BDA0001524888630000092
A unit normal vector pointing to the outside of the flow field at the inlet of the engine; mfMach number at the inlet of the engine; p is a radical offIs the pressure value at the inlet of the engine, pfIs the fluid density at the engine inlet; gamma is gamma-ReθIntermittent factors in transition models;
engine outlet boundary conditions:
for the engine outlet, the boundary conditions are also given by the engine operating conditions, which normally will be the total temperature T of the engine exhaust gases0,exAnd total pressure p0,exAs the given parameter. For external diseasesFor flow calculation, the total temperature T of the jet0,exAnd total pressure p0,exIt is the inlet condition of the flow field. By assuming a static pressure p at the outletexFrom the flow field, the jet flow satisfies the isentropic relation. Therefore, for engine outlet conditions, p is knownex，p0,ex，T0,ex：
Figure BDA0001524888630000093
Where ρ isexIs the outlet density, R is the gas constant, value 287;
then use
Figure BDA0001524888630000094
Obtaining boundary conditions of an engine outlet
Figure BDA0001524888630000095
Wherein
Figure BDA0001524888630000096
A unit normal vector pointing to the interior of a flow field at an outlet of the engine; p is a radical ofexIs the pressure value, p, of the engine outletexIs the fluid density at the engine outlet; t is0,exIs the total temperature of the engine exhaust gases.
Step 104: and updating the parameter groups by adopting a Latin square design method to obtain a plurality of variable groups. Each parameter group is corresponding to obtain a variable group. This step is a process of experimental design in the design space for the set of design variables Xi: n sets of parameter sets Xi in a design space are obtained by adopting Latin square design, and the N sets of design variable sets need CFD solution to obtain a plurality of variable sets for establishing a Kriging response surface model.
Step 105: and acquiring the nacelle resistance corresponding to each variable group according to the variable groups, and establishing a first Kriging response surface model. Obtaining the nacelle resistance corresponding to each variable group by adopting a structured grid and a three-dimensional NS equation, further obtaining the mean value of the nacelle resistance of each variable group, and establishing a first Kr according to each variable group and the mean value of the nacelle resistance corresponding to each variable groupiging response surface model fμ。
Step 106: and acquiring the variance of the nacelle resistance corresponding to each variable group according to the first Kriging response surface model, and establishing a second Kriging response surface model. First Kriging response surface model f established based on step 105μObtaining the variance corresponding to the variable group Xi by the Monte Carlo method
Figure BDA0001524888630000101
And then establishing a second Kriging response surface model according to the variable group and the variance.
Step 107: an objective function is determined. Will be provided with
Figure BDA0001524888630000102
As an objective function, wherein
Figure BDA0001524888630000104
Represents the mean value of the nacelle resistance corresponding to the ith variable group,
Figure BDA0001524888630000103
the variance of the nacelle resistance corresponding to the ith variable set is indicated.
Step 108: and predicting the mean value and the variance of the nacelle resistance by using the first Kriging response surface model and the second Kriging response surface model.
Step 109: and obtaining a variable group when the function value of the objective function is minimum, and obtaining an optimal variable group. And (4) carrying out optimization solution by using an EGO (global optimization algorithm) to obtain Xn with the minimum objective function value in the design space.
And (3) testing the predicted mean value and variance of the first Kriging response surface model and the second Kriging response surface model by using an NS equation at an Xn point, if the convergence criterion is met, taking Xn as an optimal appearance parameter, if the convergence criterion is not met, increasing a design variable sample point group Xj, namely increasing the number of parameters in a parameter group, merging Xj into Xi to form a new Xi, and repeating the steps 105 to 109 until the convergence criterion is met.
Step 1010: and determining the shape of the natural laminar flow nacelle according to the parameters in the optimal variable group.
Since conventional numerical simulation usually constructs a grid for a single aircraft, each grid point is iteratively calculated in the process until all calculation points satisfy a convergence condition. However, for numerical simulation of multiple aircrafts, especially when complex aerodynamic phenomena such as airflow viscosity, wave system interference, vortex generation, development and dissipation are considered, the amount of calculation grids is increased sharply, conventional industrial personal computers, servers and the like cannot provide enough resources for calculation, and special calculation workstations are high in cost, so that large-scale calculation is not practical, and calculation efficiency is also influenced. The development of a new calculation method with strong operability and low calculation resource consumption is an effective means for improving the numerical simulation efficiency of the similar flight formation problem. Therefore, the boundary conditions of a plurality of grids are set based on the wake vortex transmission method, the wake vortex field calculated under the free boundary condition is used as the boundary condition of the rear computing grid, the simulation object is divided into three sub-problems, the computing grids and the turbulence models with different densities are set up aiming at different objects, and the consumption of computing resources is reduced while the simulation precision is ensured. The spatial grid updating needs a corresponding dynamic grid technology, and a disturbance-based transfinite difference value (TFI) method is adopted to generate a deformed grid.
FIG. 2 is a schematic structural diagram of a system for determining the shape of a nacelle according to the invention. As shown in fig. 2, the system includes:
a parameterization module 201, configured to parameterize a section of a nacelle to be improved by using a CST method to obtain a plurality of parameter sets; each parameter group comprises different values of a plurality of parameters; the nacelle to be improved is a non-layer fluidization nacelle;
a transition occurrence position obtaining module 202 for passing gamma-ReθThe transition model acquires the transition position of the natural laminar flow nacelle;
and the boundary condition acquisition module 203 is used for acquiring boundary conditions of an inlet of the air inlet and an outlet of the engine. The boundary condition obtaining module 203 specifically includes:
an inlet boundary condition acquisition unit for acquiring inlet boundary condition of air inlet channel based on
Figure BDA0001524888630000111
Obtaining boundary conditions of inlet of air inlet passage
Figure BDA0001524888630000112
Wherein
Figure BDA0001524888630000113
A unit normal vector pointing to the outside of the flow field at the inlet of the engine; mfMach number at the inlet of the engine; p is a radical offIs the pressure value at the inlet of the engine, pfIs the fluid density at the engine inlet; gamma is gamma-ReθIntermittent factors in transition models;
an engine outlet boundary condition acquisition unit for obtaining a boundary condition based on
Figure BDA0001524888630000121
Obtaining boundary conditions of an engine outlet
Figure BDA0001524888630000122
Wherein
Figure BDA0001524888630000123
A unit normal vector pointing to the interior of a flow field at an outlet of the engine; p is a radical ofexIs the pressure value, p, of the engine outletexIs the fluid density at the engine outlet; t is0,exIs the total temperature of the engine exhaust gases.
A variable group obtaining module 204, configured to update the parameter groups by using a latin square design method to obtain a plurality of variable groups; each parameter group correspondingly obtains a variable group;
a nacelle resistance obtaining module 205, configured to obtain, according to the multiple variable groups, a nacelle resistance corresponding to each variable group; the nacelle resistance obtaining module 205 obtains the nacelle resistance corresponding to each variable group using a structured grid and a three-dimensional NS equation.
A first Kriging response surface model building module 206, configured to build a first Kriging response surface model according to the plurality of variable groups and the corresponding nacelle resistance;
a variance obtaining module 207, configured to obtain, according to the first Kriging response surface model, a variance of nacelle resistance corresponding to each variable group;
a second Kriging response surface model building module 208, configured to build a second Kriging response surface model according to the multiple variable groups and the corresponding variances;
an objective function determination module 209 for determining an objective function
Figure BDA0001524888630000124
Wherein
Figure BDA0001524888630000126
Represents the mean value of the nacelle resistance corresponding to the ith variable group,
Figure BDA0001524888630000125
representing the variance of the nacelle resistance corresponding to the ith variable group;
a prediction module 2010 for predicting a mean and a variance of nacelle resistance using the first and second Kriging response surface models;
an optimal variable group obtaining module 2011, configured to obtain a variable group when the function value of the target function is minimized, so as to obtain an optimal variable group;
and a natural laminar flow nacelle shape determining module 2012, configured to determine a shape of the natural laminar flow nacelle according to the parameters in the optimal variable group.
The system further comprises:
the judging module is used for obtaining a variable group when the function value of the objective function is minimum, detecting the mean value of the nacelle resistance predicted by the first Kriging response surface model and the variance of the nacelle resistance predicted by the second Kriging response surface model at the optimal variable group according to an NS equation, judging whether the convergence standard is met or not, and obtaining a first judging result;
a final optimal variable group determination module, configured to, when the first determination result indicates that a convergence criterion is satisfied, take the optimal variable group as a final optimal variable group;
and the parameter updating module is used for increasing parameters in the parameter group when the first judgment result shows that the convergence standard is not met, and returning to the step of acquiring the nacelle resistance corresponding to each variable group according to the plurality of variable groups.
The specific implementation mode is as follows:
the initial shape nacelle is a non-laminar flow nacelle shape, and the design state is that the Mach number Ma is 0.76, the attack angle a is 2.0, and the design Reynolds number Re is 1.0 multiplied by 107Calculating the turbulence Tu to be 0.3%, the reference length of the nacelle Reynolds number to be 3.25m, and the reference area to be about 288m2The objective function and constraints are expressed as follows:
Figure BDA0001524888630000131
CDin order to provide for the resistance of the nacelle,
Figure BDA0001524888630000132
is the variance of the nacelle resistance and,
Figure BDA0001524888630000133
is the maximum thickness of the section of the nacelle,
Figure BDA0001524888630000134
the maximum cross-sectional thickness of the initial profile of the nacelle.
Referring to the specific embodiment, fig. 3 is a schematic external view of the nacelle with natural laminar flow according to the present invention, as shown in fig. 3. The design variables as few as possible and the design space as large as possible are important pursuit indexes of the parameterization method, and the parameterization method based on class function/class function transformation (CST) proposed by Kulfan and the like of boeing corporation has higher precision and clear geometric meaning in a plurality of parameterization methods, and simultaneously has few control parameters. A typical profile of the nacelle was selected for parameterization by the CST method in the study herein. The design of the engine lip section size, the inner molded surface and the like has obvious influence on the air inlet condition of the engine, the design is mainly determined by engine parameters, the improvement is mainly carried out aiming at the outer surface of a nacelle, and in order to save calculation resources, half-mode calculation is selected. The shape of the nacelle is parameterized, three typical sections of the upper side, the lower side and the lower side are parameterized by adopting a six-stage CST (n is 6) method, 21 design variables are counted, the modified shape of the nacelle is obtained through incremental difference, and the precise description of the shape characteristics of the nacelle can be realized by using fewer parameters.
The resistance of the improved nacelle is obviously reduced, and the resistance coefficient of the improved nacelle is obviously reduced by 25.2 percent, and the pressure difference resistance component and the friction resistance component of the improved nacelle are reduced by 0.7 resistance unit and 2.7 resistance unit respectively. FIGS. 3 and 4 are graphs comparing two typical section (section) generatrices of the upper and lower portions of the nacelle, and it can be seen from the section shape comparison graph that the radius of the front edge of each section is reduced, the relative position of the maximum thickness is greatly moved backwards, and the maximum relative thickness is slightly increased due to the restriction of the constraint condition.
FIGS. 4 and 5 are comparative views of two typical sectional (profile) bus bars above and below the nacelle, and FIG. 4 is a comparative view of the upper profile bus bar of the nacelle to be modified and the modified natural laminar flow nacelle of the present invention; FIG. 5 is a comparison of the lower profile generatrix of the nacelle to be modified of the present invention with the modified natural laminar flow nacelle; according to the cross-section shape comparison graph, after optimization, the radius of the front edge of each cross section is reduced, the relative position of the maximum thickness is greatly moved backwards, and the maximum relative thickness is slightly increased due to the limitation of constraint conditions.
FIG. 6 is a graph showing a comparison of the distribution of the coefficients of frictional resistance of the upper, lower and side surfaces of the nacelle to be modified and the modified natural laminar flow nacelle according to the present invention; the three section transition positions of the initial appearance are positioned near 20% chord length, meanwhile, due to the existence of the attack angle, the upper section transition position is close to the front, the lower section transition position is close to the rear, the lateral section transition position is positioned between the upper section transition position and the lower section transition position, the optimized result shows that the transition positions of the three sections are greatly moved back to the vicinity of 45% -55% chord length, and the influence rule of the attack angle on different sections is consistent with that of the initial nacelle.
FIGS. 7 and 8 are photographs comparing the coefficient of friction of the surface of the initial nacelle and the modified nacelle, and FIG. 7 is a cloud of the coefficient of friction of the surface of the nacelle to be modified according to the present invention; FIG. 8 is a cloud chart of the coefficient of friction resistance of the surface of the nacelle with natural laminar flow after the improvement of the invention. The initial nacelle is close to the front in the maximum relative thickness position and the curvature of the head is large, the transition position is close to the front by 20%, the optimized maximum thickness position moves backwards, the transition position moves backwards by about 50% to a large extent, and the effect of weakening the friction resistance is obvious.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. A method of determining a natural laminar flow nacelle profile, the method comprising:
parameterizing the section of the nacelle to be improved by adopting a CST method to obtain a plurality of parameter sets; each parameter group comprises different values of a plurality of parameters; the nacelle to be improved is a non-layer fluidization nacelle;
by gamma-ReθThe transition model acquires the transition position of the natural laminar flow nacelle;
acquiring boundary conditions of an inlet of an air inlet channel and an outlet of an engine;
updating the parameter groups by adopting a Latin square design method to obtain a plurality of variable groups; each parameter group correspondingly obtains a variable group;
obtaining the nacelle resistance corresponding to each variable group according to the variable groups;
establishing a first Kriging response surface model according to the variable groups and the corresponding nacelle resistance;
obtaining the variance of the nacelle resistance corresponding to each variable group according to the first Kriging response surface model;
establishing a second Kriging response surface model according to the variable groups and the corresponding variances;
determining an objective function
Figure FDA0001524888620000011
Wherein
Figure FDA0001524888620000015
Represents the mean value of the nacelle resistance corresponding to the ith variable group,
Figure FDA0001524888620000012
representing the variance of the nacelle resistance corresponding to the ith variable group;
predicting the mean value and the variance of the nacelle resistance by using the first Kriging response surface model and the second Kriging response surface model;
obtaining a variable group when the function value of the objective function is minimum, and obtaining an optimal variable group;
and determining the shape of the natural laminar flow nacelle according to the parameters in the optimal variable group.
2. The method according to claim 1, wherein the obtaining boundary conditions of the inlet of the air intake passage and the outlet of the engine specifically comprises:
according to
Figure FDA0001524888620000013
Obtaining boundary conditions of inlet of air inlet passage
Figure FDA0001524888620000014
Wherein
Figure FDA0001524888620000021
A unit normal vector pointing to the outside of the flow field at the inlet of the engine; mfMach number at the inlet of the engine; p is a radical offIs the pressure value at the inlet of the engine, pfIs the fluid density at the engine inlet; gamma is gamma-ReθIntermittent factors in transition models;
according to
Figure FDA0001524888620000022
Obtaining boundary conditions of an engine outlet
Figure FDA0001524888620000023
Wherein
Figure FDA0001524888620000024
A unit normal vector pointing to the interior of a flow field at an outlet of the engine; p is a radical ofexIs the pressure value, p, of the engine outletexIs the fluid density at the engine outlet; t is0,exIs the total temperature of the engine exhaust gases.
3. The method according to claim 1, wherein the obtaining the nacelle resistance corresponding to each variable group from the plurality of variable groups specifically comprises:
and acquiring the nacelle resistance corresponding to each variable group by adopting a structured grid and a three-dimensional NS equation.
4. The method according to claim 3, wherein the structured grid comprises in particular:
setting a plurality of grid boundary conditions based on a wake vortex transmission method, and taking a wake vortex field obtained by calculation under the free boundary condition as the boundary condition of a rear calculation grid;
dividing the simulation object into a plurality of subproblems, and setting up calculation grids and turbulence models with different densities for different objects.
5. The method of claim 1, wherein obtaining the variable set that minimizes the function value of the objective function further comprises, after obtaining an optimal variable set:
at the optimal variable group, detecting the mean value of the nacelle resistance predicted by the first Kriging response surface model and the variance of the nacelle resistance predicted by the second Kriging response surface model according to an NS equation, and judging whether the convergence standard is met or not to obtain a first judgment result;
when the first judgment result shows that the convergence criterion is met, taking the optimal variable group as a final optimal variable group;
and when the first judgment result shows that the convergence standard is not met, increasing the parameters in the parameter group, and returning to the step of acquiring the nacelle resistance corresponding to each variable group according to the plurality of variable groups.
6. The method according to claim 1, wherein the obtaining of the variable set that minimizes the function value of the objective function to obtain an optimal variable set specifically comprises:
and performing optimization solution by adopting an EGO (global optimization algorithm) to obtain a variable group when the function value of the objective function is minimum.
7. A system for determining the profile of a nacelle with natural laminar flow, the system being adapted for use in the method of any of claims 1-6, the system comprising:
the parameterization module is used for parameterizing the section of the nacelle to be improved by adopting a CST method to obtain a plurality of parameter sets; each parameter group comprises different values of a plurality of parameters; the nacelle to be improved is a non-layer fluidization nacelle;
a transition occurrence position acquisition module for passing gamma-ReθThe transition model acquires the transition position of the natural laminar flow nacelle;
the boundary condition acquisition module is used for acquiring boundary conditions of an inlet of an air inlet channel and an outlet of an engine;
a variable group obtaining module, configured to update the parameter groups by using a latin square design method to obtain a plurality of variable groups; each parameter group correspondingly obtains a variable group;
the nacelle resistance acquiring module is used for acquiring nacelle resistance corresponding to each variable group according to the variable groups;
the first Kriging response surface model building module is used for building a first Kriging response surface model according to the multiple variable groups and the corresponding nacelle resistance;
the variance obtaining module is used for obtaining the variance of the nacelle resistance corresponding to each variable group according to the first Kriging response surface model;
the second Kriging response surface model building module is used for building a second Kriging response surface model according to the multiple variable groups and the corresponding variances;
an objective function determination module for determining an objective function
Figure FDA0001524888620000041
Wherein
Figure FDA0001524888620000048
Represents the mean value of the nacelle resistance corresponding to the ith variable group,
Figure FDA0001524888620000042
representing the variance of the nacelle resistance corresponding to the ith variable group;
the prediction module is used for predicting the mean value and the variance of the nacelle resistance by utilizing the first Kriging response surface model and the second Kriging response surface model;
an optimal variable group obtaining module, configured to obtain a variable group when a function value of the objective function is minimized, and obtain an optimal variable group;
and the natural laminar flow nacelle shape determining module is used for determining the shape of the natural laminar flow nacelle according to the parameters in the optimal variable group.
8. The system of claim 7, wherein the boundary condition obtaining module specifically includes:
an inlet boundary condition acquisition unit for acquiring inlet boundary condition of air inlet channel based on
Figure FDA0001524888620000043
Obtaining boundary conditions of inlet of air inlet passage
Figure FDA0001524888620000044
Wherein
Figure FDA0001524888620000045
A unit normal vector pointing to the outside of the flow field at the inlet of the engine; mfMach number at the inlet of the engine; p is a radical offIs the pressure value at the inlet of the engine, pfIs the fluid density at the engine inlet; gamma is gamma-ReθIntermittent factors in transition models;
an engine outlet boundary condition acquisition unit for obtaining a boundary condition based on
Figure FDA0001524888620000046
Obtaining boundary conditions of an engine outlet
Figure FDA0001524888620000047
Wherein
Figure FDA0001524888620000051
A unit normal vector pointing to the interior of a flow field at an outlet of the engine; p is a radical ofexIs the pressure value, p, of the engine outletexIs the fluid density at the engine outlet; t is0,exIs the total temperature of the engine exhaust gases.
9. The system of claim 7, wherein the nacelle resistance acquisition module acquires the nacelle resistance for each variable set using a structured grid and a three-dimensional NS equation.
10. The system of claim 7, further comprising:
the judging module is used for obtaining a variable group when the function value of the objective function is minimum, detecting the mean value of the nacelle resistance predicted by the first Kriging response surface model and the variance of the nacelle resistance predicted by the second Kriging response surface model at the optimal variable group according to an NS equation, judging whether the convergence standard is met or not, and obtaining a first judging result;
a final optimal variable group determination module, configured to, when the first determination result indicates that a convergence criterion is satisfied, take the optimal variable group as a final optimal variable group;
and the parameter updating module is used for increasing parameters in the parameter group when the first judgment result shows that the convergence standard is not met, and returning to the step of acquiring the nacelle resistance corresponding to each variable group according to the plurality of variable groups.
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